HEAT LOSS IN ANIMALS

Some animals help regulate their body temperature by heat loss through their ears. Choose an animal, it can be an extinct animal, and research how it absorbs and emits heat.

Thermoregulation

Thermoregulation: is the process that allows the human body to maintain its core internal temperature.

Jack Rabbits live in the desert, where they're exposed to extremely hot daytime temperatures. The Jack Rabbit has a special biological adaptation that enables it to keep cool by adjusting its core body temperature by releasing heat from its oversized ears.

The Jack Rabbit’s large ears provide an expansive area of exposed skin loaded with blood vessels. When the surrounding air temperature is slightly below the rabbit’s body temperature, as when it retreats from hot desert sun into shade, the blood vessels in the outer part of its ears widen. This increases the surface-area-to-volume ratio of the vessels, a response that favours heat loss to the surrounding air, lowering the rabbit’s body temperature. This reduces the need for evaporative cooling mechanisms, such as panting or sweating and is an important water conservation technique given the Jack Rabbit's arid habitat. At air temperatures around 30° Celsius, convection from the Jack Rabbit's ears can shed all of the animal’s excess heat.

EXCERPT

"Blood flow to the ear pinnae [outside portion of the ear] is curtailed at ambient temperatures of between 1.4° and 24.0° C, which minimizes heat loss across the pinnae and allows the surfaces of erect pinnae to approach ambient temperature. The pinnae are warmed by steady or pulsatile vasodilation in some animals when the ambient temperature is between 1° and 9° C below body temperature, a response favouring heat loss. When ambient temperature exceeds body temperature by 4° to 5° C, the pinnae are circulated with blood cooler than ambient temperature; this response favours heat influx." (Hill and Vegth 1976:436)

"Convection from the ears...could account for the loss of over 100% of the animal's metabolic heat at an air temperature of 30°C. If air temperature exceeds body temperature, the animal must either store heat or resort to the evaporation of water." (Wathen et al 1971:1030)

"Many desert animals have large ears, and the jack rabbit is no exception. It has been suggested that large ears, with their network of blood vessels, may serve to radiate heat to the sky while the animal is resting in the shade, so helping to lower its body temperature." (Foy and Oxford Scientific Films 1982:165)

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